The present invention relates to an inner hand as an orthopedic fitting part, made of a thermoplastic, for accommodating a hand mechanism, having an annular groove which is made in the end portion of the hand and into which a ring which fixes the inner hand on the hand mechanism is inserted.
A prior art inner hand is produced from PVC, has a uniformly continuous wall thickness of the same material hardness and serves to cover and give shape to the hand mechanism. The annular groove is designed as a round groove in which a beaded ring is inserted.
The shape and proportion are responsible for material stresses, which arise in particular in the intermediate region between the thumb and the index finger as well as in the back part of the hand. It is this which is the cause of uneconomical energy consumption in connection with a reduced opening width between the thumb and the index finger. Only low mechanical strength is obtained at the utilization points of the thumb, index finger and middle finger and in the intermediate region between the thumb and the index finger. However, the material specific dimensional stability leads to cyclic volume displacements, especially in the end portion of the hand so that it is impossible to guarantee effective protection of the mechanism against sweat and other kinds of contamination. The homogeneous, intrinsically firm and inflexible PVC material results in relatively poor efficiency with the disadvantages mentioned above, which despite this fact have hitherto been accepted as a justifiable compromise.